The present invention relates, in general, to a stator for an electric drive, and more particularly to a stator having winding end portions masked by insulating material. The present invention is also directed to a method of potting winding end portions of a stator for an electric drive.
German patent specification DE 1118342 describes a stator having winding end portions which are covered by an insulating tape, whereby a tape area, which projects beyond the edge of the winding end portion, is turned inwardly in axial direction over the winding end portion toward the pole bore to thereby insulate the winding end portion.
German utility model 1 797 835 describes a protection of the winding end portions through pre-formed caps of insulating material, whereby the caps are placed over the winding end portions. Such caps are made in particular from a rigid and dust-proof textile material and cast with an insulating material.
Insulation and protection of winding end portions of stators for an electric drive through casting with insulating material, especially resin, have been proposed; However, conventional insulating processes are disadvantageous because of the need for usage of conventional casting tools of steel or silicone. The casting process is executed by lining the casting mold with parting agents, installing the casting mold, dismantling the casting mold after the casting process, and subsequently cleaning the casting mold. This casting process is time-consuming and is characterized by significant nonproductive periods, when stators for electric drives are cast, resulting in an increase of production costs. Another drawback associated with this conventional process to cast stators is the insufficient coverage with insulating casting material of wires or coil components that may be too closely disposed to the casting tool. As a consequence, oftentimes, these areas have problems as far as strength is concerned.
It would therefore be desirable and advantageous to provide an improved stator and to provide an improved process of making a stator, to obviate prior art shortcomings.
According to one aspect of the present invention, a stator for an electric drive includes a stator housing configured in the form of a stack of laminations and having opposite winding end portions and a stator bore which defines an axis; a pair of tubular insulators for respectively abutting the axis-confronting inner surface of the winding end portions; a cooling jacket, arranged in circumferential direction of the stator housing, wherein one tubular insulator in concert with an end face of the stator housing and the cooling jacket bounds a cavity for receiving one winding end portion, and wherein the other tubular insulator in concert with another end face of the stator housing and the cooling jacket bounds a cavity for receiving the other winding end portion; wherein insulating casting material is poured into each of the cavities to fill it out to thereby realize a potting of the winding end portions.
The present invention resolves prior art problems by utilizing the tubular insulator as lost casting mold for potting the winding end portions of a stator so that the need for casting tools is eliminated. The use of the tubular insulator also protects the winding end portion from damage during material-removing processes, such as turning or grinding. In particular, when installing a rotor of a synchronous motor in the stator bore, the permanent magnets of the rotor cause strong magnetic forces that tend to move the rotor out of the center of the bore. As a consequence, when using conventional insulating methods, there is a risk of contact that may lead to a damage of the winding end portion.
According to another feature of the present invention, the installation of the tubular insulator is simplified by providing the tubular insulator at its stator housing confronting end face with a centering ring for radially centering the tubular insulator in relation to the stator bore of the stator housing. Suitably, the centering ring is formed integrally with the tubular insulator.
According to another feature of the present invention, the stator may have circular cover slides which engage slots of the stator housing at one end face thereof to mask the slot structure, and are arranged in surrounding relationship to the stator bore and project beyond the end faces of the stator housing, wherein the centering rings support the tubular insulators against the cover slides and seal a junction between the tubular insulators and the end faces of the stator housing in radial direction by bearing against the cover slides and in axial direction by bearing upon the slot flanks.
According to another feature of the present invention, the tubular insulator has a stator housing distal end provided with a reinforcement that enhances stability and serves as measure for a required filling height during pouring of the casting material.
According to another aspect of the present invention, the tubular insulator may be used as lost casting mold for potting the winding end portions with casting material, whereby the tubular insulator is centered in relation to the stator bore by abutting the tubular insulator against the bore-confronting inner surface of the winding end portion such that the tubular insulator bounds a cavity in concert with an end face of the stator housing and a cooling jacket, arranged in circumferential direction of the stator housing, for receiving the winding end portion, with the cavity being filled out with insulating casting material.
According to still another aspect of the present invention, a method of potting winding end portions of a stator for an electric drive includes the following steps: centering a tubular insulator in relation to a stator bore by abutting the tubular insulator against a bore-confronting inner surface of a winding end portion; forming a cavity for receiving the winding end portion, with the cavity being bounded by the tubular insulator in concert with an end face of a stator housing and a cooling jacket, arranged in circumferential direction of the stator housing; and filling the cavity with insulating casting material.